CDC42 controlled apical-basal polarity regulates intestinal stem cell to transit amplifying cell fate transition via YAP-EGF-mTOR signaling

Epithelial polarity is controlled by a polarity machinery including the Rho GTPase CDC42 and Scribble/PAR. By using intestinal stem cell (ISC)-specific deletion of CDC42 in Olfm4-IRES-eGFPCreERT2;CDC42flox/flox mice, we found that ISC-initiated CDC42 loss caused a drastic hyper-proliferation of transit amplifying (TA) cells and disrupted epithelial polarity. CDC42-null crypts displayed expanded TA cell and diminished ISC populations, accompanied by elevated hippo signaling via YAP/TAZ - Ereg and mTOR activation, independent from canonical Wnt signaling. YAP/TAZ conditional knockout restored the balance of ISC/TA cell populations and crypt proliferation but did not rescue the polarity in CDC42-null small intestine. mTOR or EGFR inhibitor treatment of CDC42 KO mice exhibited similar rescuing effects without affecting YAP/TAZ signaling. Inducible ablation of Scribble in intestinal epithelial cells mimics that of CDC42 KO defects including crypt hyperplasia and hippo signaling activation. Mammalian epithelial polarity regulates ISC and TA cell fate and proliferation via a hippo-Ereg-mTOR cascade. 1 control, 1 mutant, 1 rescue